'Casey Jones Rides Vanity' by Marion Holland (1964)

'Casey Jones Rides Vanity' was illustrated by Marion and her daughter Rebecca. From the jacket flap: "Casey's real name was Katherine Corinne, which made her K. C. Jones. Somehow the name Casey was more appropriate for a girl who was growing so fast that her riding boots were too small and her arms stuck out two inches below the cuffs of her rat-catcher. But if there was anything worse than growing out of your clothes, Casey thought, it was growing out of your pony. "It was hard to imagine selling Top. It would be like selling a member of your family, although there were times when Casey wouldn't have minded parting with her younger sister, Patty. She hated to think about losing Top, but she just had to have a horse her size. Then at the first horse show of the season Casey saw the horse she wanted. Vanity Fair was a clear golden mare with the most beautiful head Casey had ever seen. "What happened to Casey and Vanity during the eventful summer that followed is a story that all who love horses, as well as those who can sympathize with Casey's growing pains, will enjoy."